Production and characterization of antisera to synthetic 1-34 human parathyroid hormone fragments: possible implications for the correctness of proposed structures.

Antisera were raised to 1-34 hPTH-B and to 1-34 hPTH-N. In the assays utilizing antisera to 1-34 hPTH-B the relative affinity of 1-84 hPTH was correlated with the activity displayed by 1-34 hPTH-N. The activity of 13-34 hPTH-B was always higher than that of 1-12 hPTH, but both peptides displaced most of the radioiodinated 1-34 hPTH-B from the antiserum. This may be due to the fact that the 1-12 and 13-34 fragments contain a homologous sequence: 6--10 (-GlN-Leu-Met-His-AsN-) and 29--33 (-GlN-Leu-Val-His-AsN-). It was possible to develop a heterologous radioimmunoassay using anti-(1-34 hPTH-B) antiserum and [125I]1-34 hPTH-N with favourable properties: complete cross-reactivity of 1-84 hPTH and high sensitivity (less than 10-14 mol/tube). All antisera to 1-34 hPTH-N were characterized by a high reactivity towards 1-34 bPTH and a higher avidity for 1-84 hPTH than for 1-34 hPTH-B. In all assays using either antisera to 1-34 hPTH-B or antisera to 1-34 hPTH-N 19-24 hPTH-B was completely inactive. In accordance with our previous observation that position 30 in native hPTH is probably occupied by an aspartic acid residue, the present study seems to indicate that position 28 or 30 is indeed represented incorrectly by the structure of 1-34 hPTH-B.